The Childhood Development after Cochlear Implantation (CDaCI) Study is a multisite, prospective investigation of a large and diverse cohort of US children with cochlear implants. Our primary objective is to evaluate the effect of variables that influence language learning after implantation. Success in spoken language is a matter of success flowing between multiple spheres of development. Thus our aims are driven by hypotheses that relate variability in post-implant language outcome to environmental, social, interventional, and biological influences. A major challenge in such early childhood research relates to the reliable elicitation of communication and linguistic data. We address this task with hierarchical measures and video analytic techniques that allow us to track communicative skills as they emerge. We continue to build on this research experience to examine how language skills unfold in children participating in the study, evaluating their: 1. expressive & receptive language, 2. speech production, 3. speech recognition, 4. cognitive skills, 5. social interaction & behavior, 6. relationships with family members, and 7. health-related quality of life. CDaCI Study participants consist of children who received a cochlear implant (CI) before the age of 5 years (n=188) and a control group (n=97) of normal hearing (NH) age-mates. Average ages at enrollment were 2.2 years (CI) and 2.3 years (NH). So, as CDaCI participants began the study as preschoolers, they will now embark on their middle school experience, entering high school over the next five years. Retention rates for ongoing data accrual are 85% for CI children and 84% for NH children, although all data collected over the past 8+ years have been included in published analyses. Despite wide recognition of the benefits of early cochlear implantation, there remains equipoise with respect to clinical, rehabilitative, and educational strategies that enable cochlear implant technology to be used to its fullest potential for language acquisition. Modifiers of linguistic outcome become even more compelling as CI children face the performance and social demands of their early teens. This prospective, multidimensional study with concurrent controls offers prospects for novel, generalizeable insights into the sources of variation in language learning and the psychosocial outcomes observed after early cochlear implantation. Economic impact, crucial to decision-making in an era of healthcare reform, will be assessed with longitudinal cost data that are merged with outcomes reported by participants and their parents.